1. Field of the Invention
The present invention generally relates to automobile wheels which are equipped with a decorative overlay. More specifically, this invention relates to a heat-resistant overlay for a standard steel automobile wheel, in which the overlay is preferably formed from a high impact plastic and is equipped with a heat-resistant spacing element that serves to fill voids between the overlay and the wheel, so as to enable the overlay to be attached as a unitary assembly to the wheel.
2. Description of the Prior Art
Chrome-plated aluminum wheels have become very popular, particularly with both sports cars and prestigious automobiles. However, the vast majority of wheels produced in the automotive industry are standard steel wheels which are not stylized to enhance their appearance, and therefore have minimal aesthetic appeal, even if painted or chrome plated. As a result, standard steel wheels are equipped with an ornamental wheel cover in order to cover their outboard surface. While many wheel covers are mechanically attached, others are adhered to the outboard surface of the wheel, as illustrated by U.S. Pat. No. 3,915,502 to Connell.
Similarly, U.S. Pat. No. 3,669,501 to Derleth teaches an annular-shaped cover, or overlay, composed of a thin plastic cover, preferably formed from acrylonitrile-butadiene-styrene (ABS), which is axially spaced away from the outboard surface of the wheel to provide a cavity between the overlay and the wheel. During assembly, an adhesive foamable polyurethane is coated on the wheel, and the cover is then quickly clamped to the wheel before the polyurethane begins: to foam. As such, the wheel and the cover form a mold for the polyurethane foam, such that the polyurethane foam fills the cavity between the cover and the wheel and serves to permanently adhere the cover to the wheel.
Derleth teaches that the polyurethane foam adhesive provides a low-density, semi-resilient reinforcement for the thin gauge plastic cover while also providing sound insulation for tire and wind noise. However, it is understood by those skilled in the art that another reason for spacing the overlay's cover from the wheel surface is to avoid the deleterious effects of heat generated by the wheel and brake which would otherwise distort the plastic cover and delaminate any metal plating applied thereto. This is particularly true in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel. As a result, definite styling and design limitations are associated with the use of the overlay taught by Derleth.
Another shortcoming of the overlay taught by Derleth is that the foam adhesive is formed in situ on the wheel, necessitating that the wheel be available to the overlay manufacturer and handled during the production of the overlay, rendering a manufacturing process which is somewhat complicated and awkward, and reliant upon the continuous availability of wheels, a condition which may be impractical for just-in-time manufacturing programs. Furthermore, timing of the processing steps used in the manufacture of Derleth's overlay is critical in order to ensure that the cover is properly positioned over the wheel before the polyurethane begins to foam.
Others have taken the in situ technique of Derleth a step further by employing a process in which the entire overlay is formed in situ on the wheel. An early example of this technique is taught by U.S. Pat. No. 3,762,677 to Adams, in which a wheel is used to form a mold cavity with a mold half, and a reaction mixture is injected into the mold cavity to form a complete overlay. Variations of this process have been proposed, including U.S. Pat. No. 4,659,148 to Grill, which teaches assembling a metal retainer to the wheel over the wheel's hub area in order to space the overlay axially away from the center of the wheel, thus reducing thermal conduction from the wheel hub to the overlay. In effect, the wheel and retainer cooperate to form half of the mold required to mold the overlay.
Yet another variation is taught by U.S. Pat. Nos. 4,976,497 and 5,128,085 to Post et al., in which an insert is secured to the wheel prior to molding the overlay in situ on the wheel surface. As such, the insert and wheel together form a mold half for the overlay. According to Post et al., the insert is hollow and thereby serves to reduce the weight of the overlay. Another notable variation on the teachings of Adams is disclosed in U.S. Pat. No. 5,143,426 to Todd, in which a two step molding operation is used to form a low density base in situ on the wheel, and then a higher density plastic cover is molded in situ over the base to form a composite overlay.
In addition to their styling being limited by the adverse effects of high temperatures, the ornamental plastic overlays of the above prior art all share a common disadvantage, in that they require the use of a wheel as a mold half for the manufacture of an overlay. As noted previously, such a requirement results in a somewhat complicated and awkward production process which is reliant on the availability of wheels for the manufacture of the overlay.
Contrary to the prior art noted above, U.S. patent application Ser. No. 07/904,180 to Chase, assigned to the assignee of this invention, teaches a metal plated overlay which is formed independently and separately from the wheel to which it is to be attached. In particular, Chase teaches a method of producing a cast aluminum wheel having the aesthetic appearance of being metal plated, even in deep recesses in the wheel. The overlay which contributes to this appearance is a metal-plated plastic panel which is permanently adhered directly to the surface of the wheel and closely follows the contours of the wheel, including deep recesses such as turbine openings in the wheel. Together, the cast aluminum wheel and the metal-plated overlay form a composite cast aluminum wheel that can be provided as original equipment by automobile manufacturers. Notably, the metal plating process taught by Chase enables the overlay to extend and cover high temperature regions of the wheel which prior art overlays are incapable of withstanding. Unfortunately, the overlay taught by Chase is not adapted for use on standard steel wheels, in that the manner in which the overlay closely follows the contours of the wheel would result in an appearance which is limited by the surface contours of the steel wheel which, as noted above, has minimal aesthetic appeal.
From the above discussion, it can be readily appreciated that the prior art does not disclose an overlay for a standard steel wheel which does not involve the use of the wheel as a mold half during the production of the overlay. More particularly, the teachings of Derleth and Adams and its progeny require forming the overlay in situ on the wheel, which raises various processing disadvantages. Furthermore, the prior art overlays are limited in their appearance by the requirement that they be axially spaced and isolated from the outboard surface of the wheel in order to avoid the adverse effects of the elevated wheel temperatures.
Accordingly, what is needed is a method for manufacturing an overlay which is adapted to be attached to a standard automotive steel wheel so as to promote the aesthetic appearance of the wheel. More particularly, such a method would yield an overlay which is a discrete component which can be shipped and attached to the wheel at practically any point after the manufacture of the wheel. As such, production of the overlay is not reliant on the availability of a steel wheel, and the overlay is potentially available as an add-on item. Ideally, such an overlay could be secured directly to portions of the wheel without requiring thermal insulation between the overlay and the wheel.